Force needed to push box down incline plane

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Homework Help Overview

The discussion revolves around a physics problem involving forces acting on a block on a 20-degree incline plane. The original poster presents a scenario where a force of 86N is required to push a 120N block up the incline at constant speed, and they seek to determine the force needed to push the block down the incline at constant speed.

Discussion Character

  • Exploratory, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the forces acting on the block, including normal force and friction. There are attempts to calculate the coefficient of friction and the forces required for both upward and downward motion. Some participants seek verification of their calculations and reasoning.

Discussion Status

The conversation includes various attempts to solve the problem, with some participants providing calculations and others asking for checks on their answers. There is an exploration of the relationships between the forces involved, but no consensus has been reached regarding the final answer.

Contextual Notes

Participants mention specific values for forces and coefficients, but there is an indication of uncertainty regarding the correctness of these values and calculations. The problem setup and assumptions about constant speed and friction are also under discussion.

Physics_girl1
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Homework Statement


a) if a force of 86N parallel to the surface of a 20 degree incline plane will push a 120N block up the plane at constant speed, what force parallel to the plane will push it down at constant speed?


Homework Equations


\SigmaF(X)=F(A)-F(fr)-mgcos\vartheta=0
\SigmaF(Y)=F(n)-mgsin\vartheta=o
where F(A)= force applied, F(fr)= friction force, F(n)= normal force, mg=weight, F(X)= sum of forces in x direction, and F(Y)- sum of forces in y direction


The Attempt at a Solution


normal force=41.0424
friction force=26.73
my answer is -86.0331
 
Last edited:
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my coefficient of friction for this problem=.652
 
could someone please check my answers?
 
Physics_girl1 said:

Homework Statement


a) if a force of 86N parallel to the surface of a 20 degree incline plane will push a 120N block up the plane at constant speed, what force parallel to the plane will push it down at constant speed?


Homework Equations


\SigmaF(X)=F(A)-F(fr)-mgcos\vartheta=0
\SigmaF(Y)=F(n)-mgsin\vartheta=o
where F(A)= force applied, F(fr)= friction force, F(n)= normal force, mg=weight, F(X)= sum of forces in x direction, and F(Y)- sum of forces in y direction


The Attempt at a Solution


normal force=41.0424
friction force=26.73
my answer is -86.0331

Physics_girl1 said:
my coefficient of friction for this problem=.652

Physics_girl1 said:
could someone please check my answers?

Hi
Writing out the equation for the force to push up the block with constant speed, i.e. net force is zero.
120 sin 20(component of weight along incline) +120 cos 20 * u(Force of friction, u is the coefficient)=86
solve for u
u=0.399
Now for the second part:
120 sin 20 +F=120 cos 20 *u
F=120 sin 20-120 cos 20 *u
F=3.9 N
dos this help?
 

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